This is another chromosome abnormality. While Down’s syndrome is due to autosomal abnormality, Kleinfelter’s syndrome is due to the abnormality of sex chromosomes.
Individuals exhibit abnormality only during adulthood, childhood being normal. Affected individuals are males. The symptoms are-
(i) Absence of spermatogenesis
(ii) Excessive secretion of gonodotropins in the urine
(iii) Genitalia underdeveloped
(iv) Sparse body hair
(v) Some degree of breast development
(vi) Mental retardation
(vii) Effeminate behaviour
Cytological study of these individuals shows that they are basically males, but have an extra X chromosome- they are XXY. They have a total of 47 chromosomes instead of 46. This abnormality occurs during meiosis due to the non separation of the two X chromosomes. As a result, some eggs will have 2X chromosomes instead of one. If such an egg (22 autosomes + 2X chromosomes) is fertilized by a normal sperm (22+Y) the resultant individual will be a Kleinfelter’s Syndrome.
This is seen in females and is characterized by-
(i) Dysgenesis of gonads
(ii) Sexual infantilism
(iii) Webbed neck
(iv) Prominent ears
(v) Increased carrying angle of arms (cubitus valgus)
(vi) Dystrophy of the nails and hypoplastic nipples
Individuals with Turner’s syndrome have only 45 chromosomes i.e., 44 (22 pairs) autosomes and only one X chromosome instead of the normal 2 X chromosomes (XO). This arises due to meiotic abnormality when an egg does not receive any X chromosome. If such an egg is fertilized by a sperm carrying an X chromosome, the result will be 44 autosomes and only one X chromosome.
One in 5000 births ( in west) is estimated to be affected by this syndrome.